In its broader aspects, the invention is not limited to a complete system such as was described in the foreging Abstract, but to a device for substitution of signals. Devices for comparing the amplitudes of two signals are well known but they are plagued with the problem that the device must work over a wide range of signal amplitudes. At low amplitudes the signal-to-noise ratio is unacceptable unless the bandwidth is narrow. A narrow bandwidth increases the time required for the device to settle to a stable output indication. This slows the test process especially if tests are to be made at least about 200 selected frequencies between, for example, 1 GHz and 18 GHz.
The primary object of this invention is to overcome the aforesaid disadvantage.
Other objects and advantages of this invention will appear as this description proceeds, especially advantages relating to improving the automation, speed and accuracy of a device of the class described.